PJM issued a warning Dec. 1 that a possible geomagnetic disturbance could impact the PJM system, but experienced no operational impacts for the duration of the event.
The warning was in effect for 6:55 a.m. to 4 p.m. Friday. No disturbance was detected, and thus, PJM operations were not affected.
Such warnings alert PJM generation and transmission operators of prescribed operations steps to take to offset possible impacts of such phenomena. When a geomagnetic disturbance (GMD) is actually identified, PJM issues a GMD Action and operates the system with more conservative power limits, in case the unexpected additional power from the geomagnetic disturbance flows on the system.
What Is a Geomagnetic Disturbance?
Geomagnetic disturbances (PDF), also known as solar magnetic disturbances, are caused by activity on the surface of the sun. They are fairly rare but pose potential impacts to the grid.
Sunspots, solar flares or other phenomena can produce large clouds of plasma, called coronal mass ejections. These ejections may induce powerful electric currents within the earth and on high-voltage transmission lines. These currents may flow up from the earth or down into the earth through grounded grid equipment, usually transformers. High levels of these currents have the potential to disrupt or damage transmission equipment.
For example, a major disturbance on March 13, 1989, caused a nine-hour power disruption in Quebec and also severely damaged a transformer at the Salem Nuclear Power Plant in Salem County, New Jersey.
The Space Weather Prediction Center of the National Oceanic and Atmospheric Administration (NOAA) monitors both solar activity and the earth’s magnetic field and issues alerts and warnings to grid operators so they can prepare for the impacts of space weather events.
GMD warnings are fairly common, usually occurring several times a year, but actual GMD events are rare. The last time PJM was actually impacted by a GMD event was September 2014.
How Does PJM Help Protect Against Geomagnetic Disturbances?
When the NOAA Space Weather Prediction Center issues an alert to PJM rated above a certain threshold, PJM issues a warning to generation and transmission operators to prepare for potential impacts to equipment.
To help anticipate problems, PJM members have installed special equipment to detect and measure ground-induced currents caused by geomagnetic disturbances. PJM monitors the installed detectors at various locations. If sustained ground currents at a certain level are detected, PJM operates the system in a more conservative mode until the space weather event has ended.